Iran has reported flights by U.S. military aircraft over nuclear facilities near the borders with Afghanistan and Iraq.

Iran's state-controlled media said the overflights by U.S. aircraft were spotted near a range of nuclear facilities, including the Bushehr nuclear reactor constructed by Russia.

In late December, Teheran ordered the Iranian Air Force to shoot down unidentified aircraft flying anywhere in the country, Middle East Newsline reported. Iranian officials have accused Israel and the United States of seeking to conduct reconnaissance flights over Iran.

Iran has deployed anti-aircraft missiles around major nuclear sites, including Bushehr. So far, there have been no reports of Iranian missile fire toward U.S. or Israeli warplanes.

The U.S. reconnaissance flights were conducted as Iran was said to be accelerating its nuclear weapons programs in facilities unaccessible to the International Atomic Energy Agency.

The U.S. aircraft said to have entered Iranian air space included F-16 multi-role fighters and F/A-18 attack jets, the reports said. The Iranian media said the aircraft appeared to have been sent on reconnaissance missions over Iran's nuclear sites, particularly in the southwestern province of Khuzestan.

On Monday, the Iranian newspaper Aftab reported the entry of a U.S. fighter-jet on Jan. 1. The unidentified fighter was said to have flown at low altitude over the northeastern province of Khorrasan which borders Afghanistan.

Iran's air defense command contains aging U.S.- and Russian-origin surface-to-air missile batteries not regarded as a threat to U.S. fighter-jets. The Iranian systems include the U.S. Hawk MIM-23B, the Russian SA-2, SA-5, SA-6 as well as the shoulder-launched SA-18. Iran has sought to purchase the Russian-origin S-300PMU long-range system.